The present invention concerns valves of the type having a rotatable valve stem passing through a bonnet and having a sealing surface for engagement and disengagement with a valve seat in the valve body. Such valves are commonly used in many industries, and one such type of valve referred to as a gauge valve is illustrated in several embodiments in a brochure entitled "INDUSTRIAL VALVES AND MANIFOLDS" distributed by General Screw Products Company. Many such valves are provided with a bonnet threaded to the valve body and adapted for receiving a rotatable and axially movable valve stem, and for convenience in description are the type of valve generally referred to below.
More particularly, the present invention concerns the seals which prevent the escape of pressurized fluid from the valve body. A first seal is provided between the valve stem and the bonnet, and a second seal is provided between the valve body and the bonnet. In many prior art embodiments, this latter seal is a metal-to-metal seal formed between the end of the bonnet and the valve body, as shown, for example, in U.S. Pat. No. 4,556,196. Among other reaons, a valve with metal-to-metal seals between the bonnet and the valve body is not generally preferred for handling highly corrosive fluids. A pin hole leak past the metal-to-metal seal cannot be easily repaired, and often such a leak results in the economic loss of an entire valve.
It is well known in the art to provide an arrangement whereby the valve stem seal may be periodically further compressed. With time, such seals generally tend to lose their sealing effectiveness, and further compression of the seal can often stop fluid leakage around the valve stem. One illustration of a compressible valve stem seal is shown in U.S. Pat. No. 3,529,805.
Pliable seals between the valve stem and the bonnet, and between the bonnet and the body, are shown in U.S. Pat. No. 3,401,357. The valve body-bonnet seal arrangement described therein has not, however, been widely accepted in the industry, and compression of the valve stem seal cannot be easily accomplished. A valve body-extension member seal is disclosed in U.S. Pat. No. 3,910,553, but compression of the valve stem seal is not provided.
It is also known in the art to provide a compressible seal between a valve body and a valve stem, along with means for further compressing the seal during maintenance operations. Such a valve, however, has significant disadvantages over a valve of the type employing a valve stem seal between the bonnet and the valve stem. First, a valve of the latter type can generally be made with fewer and/or less expensive components. Second, a valve of the latter type can be easily manufactured with fireproof metal-to-metal seals for preventing fluid loss past the valve stem when the valve is in the fully open position --even if the valve stem seal is destroyed.
The disadvantages of the prior art overcome by the present invention, in improved methods and apparatus are hereinafter provided for effectively sealing fluid within a valve body.